In general, a speed control system in which a filter delay element or a dead time delay element is present in a controller or a control object is shown in FIG. 3. FIG. 3 is a block diagram showing a general speed control system.
In FIG. 3, 1 denotes a subtractor, 2 denotes a PI controller, 3 denotes a filter delay element, 4 denotes a dead time delay element, 5 denotes a mechanical system including a motor, Vr denotes a target speed, Vf denotes a speed feedback signal, and VM denotes a speed.
In a general speed control device, both a speed signal obtained from a speed sensor (not shown) and a speed signal obtained by differentiating a position signal of a position sensor (not shown) have high frequency ripple components. Also in the control system shown in FIG. 3, therefore, the speed feedback signal Vf has the high frequency ripple component, and furthermore, the phase of the filter delay element 3 or the dead time delay element 4 is delayed. For this reason, there is a problem in that the gain of the PI controller 2 is not increased and a sufficient response characteristic cannot be obtained. In order to improve such a problem of controllability, the following conventional art has been proposed.
FIG. 4 is a block diagram showing a control system according to a first conventional art. The same components in the first conventional art as those in FIG. 3 have the same reference numerals and description will be omitted, and only different components will be described. In FIG. 4, 7 denotes an adder, 8 denotes a model of a mechanical system including a motor, 9 denotes a subtractor, 10 denotes a speed observer compensator, and 14 denotes a speed observer. As shown in FIG. 4, an observer of the mechanical system is constituted and a speed estimated value of the smooth observer is set to be a speed feedback signal Vf. Consequently, a torque waveform is not disturbed so that the gain of the PI controller 2 can be increased (for example, JP-A-11-136983).
Moreover, FIG. 5 is a block diagram showing a control system according to a second conventional art. Components in the second conventional art are different from those in FIG. 3 in that a phase leading compensator 13 is added in series to a control system. In the phase leading compensator 13, if Ta and Tb are properly set to be Ta>Tb, the phase of the phase leading compensator 13 is led. Consequently, the gain of the PI controller 2 can be increased, and furthermore, a control performance can be enhanced.
In the first conventional art, however, the high frequency component of the speed feedback signal Vf is removed and a problem of the phase delay of a control loop is not solved at all. For this reason, there is a problem in that the gain of the PI controller 2 cannot be increased sufficiently.
In the second conventional art, moreover, a gain in the high frequency area of the phase leading compensator 13 is increased. Consequently, there is a problem in that an oscillation having a high frequency is apt to be caused.
In order to solve the problems, it is an object of the invention to provide a speed control device capable of removing the high frequency component of a speed feedback signal, compensating for the phase delay of a delay element so as not to generate an oscillation having a high frequency, and causing the speed of a mechanical system to follow a target speed with high precision.